Reducing Pesticide Use in Honey Bee Colonies through Sound Sampling and Treatment Procedures
We developed a sampling plan to help beekeeper monitor Varroa destructor mite infestations in honey bee colonies. From a sample of 245 adult bees, beekeepers can estimate the total mite density in a colony (mites on adults and those reproducing on pupae) using a simple chart we developed. Guidelines will be developed to help beekeepers make educated treatment decisions. Our line of bees bred for both Hygienic Behavior and Suppression of Mite Reproduction had significantly lower mite levels compared to an unselected line of bees demonstrating that this line can reduce mite loads and thus the frequency of pesticide application.
Objective 1. Develop a simple and standardized sampling plan for commercial beekeepers to help them determine the economic treatment level for Varroa destructor mites (short-term outcome).
Objective 2. Compare mite levels between our line of bees bred for both Hygienic Behavior (HYG) and Suppression of Mite Reproduction (SMR) with an unselected, commercial line of bees (short-term outcome), to demonstrate that the use of resistant bees can reduce mite loads and thus, the frequency of pesticide application (intermediate-term outcome).
Objective 3. Develop published guidelines for migratory beekeepers on making educated treatment decisions for the mite based on the sampling plan (intermediate- to long-term outcome).
Objective 1: It is relatively common for growers to sample insect pest populations in a field crop to help them make an educated treatment decision. Our goal is to encourage beekeepers to sample their bee colonies for mite pest populations in a standardized way to help them make wise treatment decisions. Such a sampling plan for a mite pest in an insect colony has never been attempted. We sampled bees from 548 colonies to obtain sufficient data to develop the sampling plan. In June and September 2005, Katie Lee, graduate student funded on this project, sampled colonies of bees for mite infestation on adult bees in 12 apiaries in MN and ND. In 2006, she sampled 10 apiaries in CA, MN and ND. In 2007, she sampled 9 apiaries in TX, MN and ND, bringing the total to 31 apiaries. She first analyzed the distribution of mites within colonies and within apiaries to determine the sample unit and sample unit size. A nested analysis of variance revealed that the colony is the largest source of variation in mite infestation level within an apiary. The sampling approach, Resampling for Validation of Sampling Plans, was used to determine the optimal number of adult bees to sample from each colony and the number of colonies to sample within an apiary. Results showed that the best method is to sample 245 bees per colony and eight colonies per apiary to achieve a precision level of 0.25. The next step was to factor in the number of mites parasitizing the brood (developing pupae) to estimate total mite loads within a colony. To achieve this, 60 colonies were sampled from eight commercial apiaries and 18 colonies from the University of Minnesota. The density of mites on a sample of adult bees was compared to the density of mites on all bees within a colony (adult and pupae) using a analysis of covariance. From this analysis, a statistical inference was drawn about the total colony mite density. In application, this analysis will allow beekeepers to sample mites on adult bees and using a conversion factor, estimate the total colony density of mites. Finally, we are developing a novel sampling device to collect the adult bees from colonies. From our talks to beekeepers at association meetings throughout the US, in South America and Europe, beekeepers are anxious to implement this sampling plan to help them make educated treatment decisions, and ultimately, realistic treatment thresholds (see Objective 3).
Objective 2. We compared colonies selectively bred for both hygienic behavior and Suppression of Mite Reproduction (HYG/SMR) with colonies bred solely for hygienic behavior (HYG) and unselected control colonies. Colonies were evaluated for strength, brood viability, removal of freeze-killed brood, honey production, mite loads on adult bees and within worker brood, and mite reproductive success on worker brood for two years in two locations (MN and ND). By autumn in both years, the HYG/SMR colonies had significantly fewer mites on adult bees and in worker brood compared to the control colonies and the HYG colonies had intermediate mite populations. Contrary to expectation, there were no differences among the lines in mite reproductive success. Further studies are required to determine if the genes and neural mechanisms that regulate the SMR trait are the same or different from those regulating hygienic behavior. We have just published a paper on these results:
Ibrahim, A., Reuter, GS, Spivak, M. 2007. Field trial of honey bee colonies bred for mechanisms of resistance against Varroa destructor. Apidologie 38: 67-76
Objective 3. When we have completed all the sampling and analysis for Objective 1, we are currently preparing guidelines for migratory beekeepers to help them make educated treatment decisions to control mites based on the sampling plan. Also, at every beekeeping association meeting Spivak, Reuter, and Lee attend, we talk to beekeepers about the importance of sampling plans and how they will improve the profit margins of their operations by not having to treat as often or extensively. We have received very favorable feedback and many say they are anxiously anticipating our results.
In 2008, Katie Lee presented her findings to the American Bee Research Conference (Sacramento, CA, January, 2008), the MN Hobby Beekeeping Association (March 2008), the International Union for the Study of Social Insects in Puerto Rico (September 2008).
Marla Spivak presented these findings to over 25 different professional and public meetings of beekeepers, scientists and the general public in 11 states across the US including 12 talks to groups within MN. She also presented in Peru, Chile, Argentina, and Nordic-Baltic countries (including Norway, Denmark, Sweden, Finland, Estonia, Latvia, Lithuania).
Impacts and Contributions/Outcomes
The North Central region of the US, particularly MN, ND and SD are the top honey producing states based on yield per colony, together producing over 30% of the total honey production for the nation. The reduction in pesticide use by beekeepers will increase the profitability of beekeeping, which is based on small and moderate-scale owner-operated farms, improve the quality of honey, a wholesome food product, and improve environmental quality by promoting honey bees, vital pollinators of our agro- and natural ecosystem.
The immediate goal of this research was to develop a sampling plan for mites within bee colonies based on well-documented sampling statistics. The long-term goal is to help beekeepers use the sampling plan to make educated treatment decisions so they can reduce pesticide application to avoid unnecessary costs, pesticide residues, and evolution of resistance of the mites to chemicals.